The present invention relates to methods for establishing the Equivalent Glycemic Load of food products, and systems for selecting food products by consumers for the management of their intake of foods that elicit glycemic responses, primarily from digestible carbohydrates.
Carbohydrates can be defined in three ways; structurally (based on molecular structure), analytically (such as, for example, as defined by Federal labeling regulations), and physiologically (based on glycemic impact).
Carbohydrates defined structurally include compounds composed of at least one basic monosaccharide unit. Under this definition, carbohydrates may be further classified as simple carbohydrates and complex carbohydrates. Simple carbohydrates are monosaccharides and disaccharides. Complex carbohydrates are polysaccharides, or large molecules composed of straight or branched chains of monosaccharides.
For labeling purposes, the Food and Drug Administration (FDA) has declared that the total carbohydrate content of a food “shall be calculated by subtraction of the sum of the crude protein, total fat, moisture and ash from the total weight of the product.” Such a measurement of carbohydrate content is not precise. For example, errors in the measurement of the food components being subtracted carry over into the determination of carbohydrate content. When measuring carbohydrate content in low-carbohydrate foods, such errors can typically be up to twenty to one hundred percent. (FAO/WHO Expert Panel on Carbohydrates. Carbohydrates in Human Nutrition/Total Carbohydrate Section; Rome, Italy (1997), http://hipocrates.univalle.edu.co/estudi/carbohyd.htm.) Additionally, since only the enumerated food components are subtracted, the FDA definition of carbohydrates includes components such as, lignin, gums, pectin and other fibers; as well as waxes, tannins, some Maillard products, flavonoids, organic acids, and polyols. Accordingly, the FDA definition of carbohydrates can include components which are not structural carbohydrates.
Carbohydrates defined physiologically are structural carbohydrates which elicit an immediate and significant impact on blood glucose and plasma insulin. Such carbohydrates are termed “glycemic carbohydrates,” “digestible carbohydrates” or “available carbohydrates.” Structural carbohydrates which do not elicit a significant impact on blood glucose and insulin are termed “non-glycemic carbohydrates.”
The Food and Drug Administration (FDA) nutritional labeling requirements do not distinguish between glycemic carbohydrates and non-glycemic carbohydrates. For example, the FDA definition lumps together sugars and starches which have an immediate and significant impact on blood glucose, with fiber which does not impact blood glucose, as well as polyols, which have little, if any, impact on blood glucose.
Glycemic carbohydrates include simple carbohydrates, and some complex carbohydrates. After consumption, simple carbohydrates are rapidly absorbed, while some complex carbohydrates are typically broken down into simple carbohydrates and then absorbed. After absorption, these simple carbohydrates can elicit a rise in blood glucose levels. Non-glycemic complex carbohydrates, and some of the compounds labeled as carbohydrates on “nutritional facts” panels under the FDA definition, are not broken down into simple carbohydrates or significantly absorbed in the small intestine, but pass into the colon where they may be fermented by bacteria, or pass through the gut intact. Molecules that are not absorbed in the small intestine do not produce a rise in blood glucose levels.
The rise in blood glucose levels immediately following absorption of glycemic carbohydrates is termed the “glycemic response.” Blood glucose is used immediately to provide energy, or is stored in the form of glycogen in the liver and muscles to be utilized when required by the body's energy demands. The transport of glucose from the blood into storage in liver and muscle cells is aided by the secretion of pancreatic insulin into the bloodstream. Any excess glucose, i.e. glucose which is not used as a source of energy or stored as glycogen, is converted to fat.
The normal blood glucose concentration in a healthy person after a four to eight hour fast is typically in a range of between 70 and 115 mg/100 ml of blood (Whitney and Rolfes 1993). During the first hour or so following a meal containing glycemic carbohydrates, blood glucose concentrations typically increase to 120 to 200 mg/100 ml. The secretion of insulin returns the glucose concentration to a baseline or controlled level usually within two hours after the last consumption of carbohydrates.
In individuals with diabetes mellitus, the body's mechanism for the control of blood glucose levels is defective. Either insulin production by the pancreas is diminished, or the ability of the body to use insulin is decreased. Without sufficient insulin, or without the ability of the insulin to move glucose into the cells, the consumption of glycemic carbohydrates, and subsequent absorption of glucose, results in glucose remaining in the blood for longer than normal.
The blood glucose levels of diabetics are highly sensitive to even small amounts of ingested carbohydrates or injected insulin. Such sensitivity can result in life threatening consequences. Blood glucose concentrations can rise to hyperglycemic levels in response to a meal. Diabetic coma may result. The blood glucose levels in diabetics can be regulated with the injection of insulin. However, too much insulin causes hypoglycemia which can result in insulin shock. Thus, a precise control of blood glucose levels within a narrow range is critical for diabetics. (National Institute of Health (NIH) News Release. Benefits of Tight Blood Sugar Control Endure for Years; February 9 (2000) (http://www.nih.gov/news/pr/feb2000/niddk-09.htm.)
The long term effects of diabetes also may result in severe consequences. These consequences may include heart disease, strokes, loss of vision due to retinal degeneration, loss of nerve and/or kidney function, and increased susceptibility to infection. Recent studies have shown that these long term effects of diabetes can be greatly reduced by keeping blood glucose levels under tight control.
Other metabolic disorders may be related to, or caused by, persistently high levels of blood glucose. Examples of such disorders include: insulin resistance; hyperinsulinism, which can lead to type II diabetes; hypoglycemia; hyperlipidemia; hypertriglyceridemia; and obesity.
The control of blood glucose levels in individuals without metabolic disorders is also highly desirable. For example, recent studies have shown that even transiently high blood glucose levels can lead to disease. For example, glucose molecules can attach to amino groups in tissue proteins and cross-link them into stiff yellow-brown compounds known as advanced glycation endproducts (AGEs). AGEs can form on the surfaces of long-lived proteins, such as collagen and elastin; in blood vessels and heart muscle; and in the crystallin of the lens. AGEs may destroy normal protein structure, inhibit protein physiological function and cause damage that leads to irreversible disease conditions in vital organs. (Vlassara H; Bucala R; Striker L; Pathogenic Effects of Advanced Glycosylation: Biochemical, Biologic and Clinical Implications for Diabetes and Aging. Lab. Invest. 70(2): 138-51 (February 1994).)
The rate of AGEs accumulation and the degree of stiffness they produce are proportional to blood glucose levels, and the length of time high levels persist.
Additionally, controlling blood glucose levels can be critical in achieving weight loss. (Ranjana Sinha et al. Prevalence of Impaired Glucose Tolerance among Children and Adolescents with Marked Obesity. New Eng J. Med 346(11):802-10 (March 2002).) For example, effective weight reduction can be achieved with a diet which minimizes blood glucose levels to the point of inducing ketosis in the body, where fat instead of carbohydrates serves as a primary fuel source. (Robert C. Atkins, MD, Dr. Atkins' New Diet Revolution (2002)).
Also, it is beneficial for athletes to control their blood glucose levels in order to enhance athletic performance. Depending on whether an athletic activity requires prolonged endurance or a brief expenditure of energy, adjusting dietary intake of glycemic carbohydrates to control blood glucose levels to suit the particular activity can benefit performance.
Accordingly, controlling blood glucose levels has many beneficial effects, most significantly including the maintenance of good health.
A system by which to rank carbohydrate-containing foods by their ability to raise blood glucose levels has been provided (Wolever et al., Journal of the American College of Nutrition 8(3):235-247 (1989)). The system provides the concept of “glycemic index” (GI).
GI is defined as the glycemic response elicited by a food containing twenty-five or fifty grams of glycemic carbohydrate expressed as a percentage of the glycemic response elicited by twenty-five or fifty grams of a glycemic carbohydrate of a standard food, such as white bread or an oral glucose solution.
The blood glucose response produced by carbohydrate foods which are digested and absorbed rapidly is fast and high. Such foods have high GIs. Conversely, carbohydrates which are digested and/or absorbed slowly release glucose gradually into the blood stream, and have low GIs.
Factors which influence the rate of digestion include food form, particle size, chemical structure (e.g., stage of ripeness), processing (e.g., degree of cooking) and macronutrient content (i.e. fat, protein and soluble fiber content). Fat and protein influence glycemic responses by delaying upper gastrointestinal transit and increasing insulin secretion, respectively.
The GI system is not easily applied by an average individual to his daily diet for several reasons.
GI assesses the glycemic carbohydrate portion of food without taking into account the food's glycemic carbohydrate density. Thus, average serving sizes are not taken into account. For example, since carrots contain a large portion of fiber and water, in addition to glycemic carbohydrate, a fifty gram glycemic carbohydrate portion of carrots is about six or seven average servings of carrots. Whereas, only a quarter cup of sugar contains a fifty gram portion of glycemic carbohydrate. That is, measure for measure, sugar contains far more glycemic carbohydrate than carrots contain. Since the glycemic carbohydrate density of food products are not taken into account, the odd result is that carrots have a GI of 71 and sugar has a GI of 65. Thus, an individual may be misled to believe that an average serving size of carrots produces a greater rise in blood glucose levels than a quarter cup of sugar.
Additionally, GI is a number without units. Therefore, an individual is not provided with a tangible measure by which to evaluate glycemic responses when making dietary choices.
Moreover, the determination of GI presents researchers with several difficulties. GI requires a determination of the glycemic carbohydrate content of both the standard food and the test food.
Most researchers obtain such content information from food composition tables or from food manufacturers' data. However, as discussed above, due to the different ways in which carbohydrate content of food is measured, such information is not uniform. The variation in the GI values of similar foods reported by researchers reflects this lack of uniformity.
To avoid relying on composition tables and manufacturers' labels, an individual researcher may measure the glycemic carbohydrate content of the food products. However, the addition of this step is cumbersome. Also, the methods used by different researchers to assess glycemic carbohydrate content vary.
Moreover, the measurement of glycemic response which relies on a measure of the glycemic carbohydrate content in a food product is inherently an approximation. That is, actual physiological conditions of the human body which may affect such responses may not fully be taken into account.
Another system which attempts to assess the glycemic responses produced by food uses the concept of glycemic load (GL). GL is calculated by multiplying the amount of glycemic carbohydrate in a portion of a test food and the GI of the food.
Accordingly, since the calculation of GL values includes determining GI values, the shortcomings and inaccuracies originating from GI values carry over to the calculation of GL values. For example, Foster-Powell et al. determine carbohydrate content for the calculation of GI values, and thus necessarily for GL values, from food composition tables. (Am J Clin Nutr 76:5-56 (2002).) Also, since the glycemic carbohydrate content in the test food is required to be measured to calculate a GL value, a further approximation is included in the calculation of the GL value.
Additionally, since GL includes the measurement of GI, the glycemic responses at either twenty-five or fifty grams of glycemic carbohydrate are used in the calculation of GL. Accordingly, it has been assumed that the functional relationship between glycemic response and glycemic carbohydrate load at either of these loads would apply to lower glycemic carbohydrate loads. That is, nutritional art and technology have not determined the actual functional relationship between glycemic response and carbohydrate portions which are less than twenty-five grams.
However, the evaluation of the glycemic responses produced by foods containing small glycemic carbohydrate portions, such as less than fifty or less than twenty-five grams, is highly important for numerous applications.
For example, as described above, the ability for diabetics to precisely control their glycemic responses is critical. It may be necessary to know the glycemic response produced by a food containing a glycemic carbohydrate portion of less than fifty grams in order to avoid insulin shock or diabetic coma.
Additionally, dieters, and those following a controlled carbohydrate lifestyle, typically consume small portions, and thus would benefit from an evaluation of glycemic responses produced by small food portions. Without such information about small portions, a dieter may choose foods which produce high glycemic responses thereby stimulating appetite.
Also, athletes typically consume small portions before engaging in athletic activities, or may consume food while performing an activity. Thus, it would be beneficial to have a method by which to assess glycemic responses of foods containing small glycemic carbohydrate portions to enhance athletic performance.
Accordingly, there is a need for the evaluation of the glycemic responses produced by food products which is easily implemented and understood by an average individual. Additionally, there is a need for a method by which researchers would be able to more easily and accurately evaluate food-produced glycemic responses. There is especially a need for a standard evaluation of glycemic responses produced by foods which contain less than twenty-five grams of glycemic carbohydrates.